Kara Zor-El is Superman's cousin and last survivor of Krypton's Argo City. She has a brash and defiant personality that she developed in response to the destruction of Krypton. Currently, she is protecting Earth in Superman's stead at his request.

There was some bizarre element where she was 17... then had a birthday... and was 17. It was strange. But not all that essential to clarify for the stories that were told, so it went largely unaddressed. No note of it in the newest issue, probably not going to come up until a who's who or bio-profile type page.

Well, technically, before the relaunch she was in her fifties since she was a teen when Superman was born. Then she was in suspended animation which halted her aging process so she retained the physical appearance of a teen-aged Kryptonian female.